Background: Metabolic syndrome is a complex disorder characterized by the coexistence of multiple risk factors, including dysglycemia, hypertension, dyslipidemia, and visceral obesity. Both metabolic syndrome and diabetes mellitus are closely associated with the onset of microvascular complications such as retinopathy, polyneuropathy, and nephropathy. Methods: This narrative review analyzed 137 studies published up to 2025, retrieved from PubMed and Crossref databases. The objective was to identify and evaluate potential biomarkers that could facilitate the early detection of microvascular complications in patients with metabolic syndrome. Results: Several biomarkers demonstrated a strong correlation with microvascular complications in individuals with metabolic syndrome. These findings suggest their potential role in early diagnosis and risk assessment. Conclusions: The identification of reliable biomarkers may enhance early detection and targeted interventions for microvascular complications in metabolic syndrome. Further research is essential to validate these markers and establish their clinical applicability in routine medical practice.

Background: Diabetic autonomic neuropathy (DAN) is a severe complication of diabetes that affects the autonomic nervous system, impacting cardiovascular, gastrointestinal, genitourinary, and other systems. This study examines the levels of three potential biomarkers—DEFA1, progranulin, and NRG4—to assess their diagnostic and prognostic value in DAN patients. Methods: This observational, single-center study included 80 patients with type 2 diabetes. Clinical data and laboratory results were collected, and serum levels of DEFA1, progranulin, and NRG4 were measured using ELISA. The presence of DAN was assessed using Ewing’s tests. Statistical analyses included t-tests, Pearson’s correlations, and ROC analysis to explore associations and the predictive values of the biomarkers. Results: Progranulin levels were significantly elevated in patients with DAN compared to those without (p < 0.05), showing a positive correlation with diabetes duration (r = 0.375; p = 0.01) and a significant predictive value for DAN (AUC = 0.666; p = 0.013). DEFA1 and NRG4 levels did not differ significantly between the groups. Progranulin was also higher in patients who were treated with sulfonylureas and GLP-1 receptor agonists and in those with coronary artery disease. Conclusions: Progranulin emerges as a potential biomarker for the presence and severity of DAN, correlating with disease duration and autonomic dysfunction. While DEFA1 and NRG4 showed no significant association, the findings underscore the importance of further exploring the inflammatory pathways in DAN. Progranulin measurement could enhance early diagnosis and personalized management of autonomic neuropathy in diabetes.

Background: Chronic low-grade inflammation plays a central role in the pathogenesis of type 2 diabetes (T2DM) and its complications. Neopterin, a marker of macrophage activation and Th1-mediated immune response, has been associated with cardiovascular disease and metabolic disorders. However, its relationship with diabetic autonomic neuropathy remains insufficiently investigated. Methods: We conducted a cross-sectional study including 129 participants (93 with T2DM and 36 with obesity without carbohydrate disturbances). Clinical, anthropometric, and biochemical assessments were performed. Cardiovascular autonomic neuropathy was evaluated using Ewing cardiovascular reflex tests and sudomotor dysfunction scoring. Neopterin concentrations were measured in serum. Correlation, ROC, and logistic regression analyses were performed. Results: Neopterin levels were not significantly different between T2DM and obesity groups. No differences were observed in patients with versus without peripheral neuropathy, nephropathy, or retinopathy. However, neopterin levels were significantly higher in individuals with cardiovascular autonomic neuropathy (p = 0.013). Neopterin correlated with cardiovascular autonomic neuropathy score, sudomotor dysfunction, fasting glucose, fasting insulin, and HOMA-IR. It showed a moderate negative monotonic correlation with eGFR (Spearman’s rho = −0.41, p< 0.001). In multivariable logistic regression adjusted for age, HbA1c, BMI, eGFR, and diabetes duration, each 1-SD increase in neopterin was associated with 2.67-fold higher odds of cardiovascular autonomic neuropathy (95% CI 1.21–5.89; p = 0.015). Conclusions: Circulating neopterin is independently associated with cardiovascular autonomic neuropathy in T2DM but not with classical microvascular complications. These findings suggest a potential role of immune-mediated mechanisms in the pathogenesis of diabetic cardiovascular autonomic neuropathy.

Background: Growth differentiation factor-15 (GDF-15) is a stress-responsive cytokine associated with inflammation, metabolic dysfunction, and cardiovascular disease. Its role as a biomarker of microvascular complications in type 2 diabetes (T2D) remains incompletely defined. Objective: To evaluate circulating GDF-15 levels and their association with microvascular complications in patients with T2D. Methods: This cross-sectional study included 160 participants divided into three groups: T2D (n = 93), obesity without carbohydrate disorders (n = 36), and healthy controls (n = 31). Microvascular complications (neuropathy, nephropathy, retinopathy) were assessed. Multivariable logistic regression and receiver operating characteristic (ROC) analysis were performed. Results: GDF-15 levels were significantly higher in T2D compared with non-diabetic individuals (267.5 ± 168.9 vs. 118.3 ± 55.5 pg/mL, p < 0.001). Higher GDF-15 was associated with neuropathy (odds ratio (OR) 1.985; 95% confidence interval (CI) 1.431–2.753) and nephropathy (OR 1.673; 95% CI 1.243–2.254) in unadjusted models. After adjustment, only nephropathy remained independently associated (OR 1.405; 95% CI 1.026–1.923). ROC analysis showed moderate discriminative ability for nephropathy (area under the curve (AUC) = 0.763). Conclusions: Circulating GDF-15 levels are significantly elevated in patients with T2D and are associated with microvascular complications, with the strongest independent association observed for diabetic nephropathy. These findings suggest that GDF-15 may represent a promising biomarker reflecting metabolic stress and risk of diabetic complications.

Background/Objectives: DEFA3 and DEFA5 are alpha-defensins, which are small cationic antimicrobial peptides that are part of the innate immune system. DEFA3 encodes human neutrophil peptide-3 (HNP-3), primarily expressed in neutrophils, while DEFA5 encodes human defensin-5 (HD-5), predominantly expressed in Paneth cells of the small intestine. Both defensins show elevated levels in diabetes and are strongly associated with diabetic nephropathy, with the highest concentrations found in patients with this complication. We evaluated serum levels of DEFA3 and DEFA5 in 160 participants (93 patients with T2DM and 67 controls without carbohydrate disturbances) and their associations with diabetic nephropathy, as well as peripheral and cardiac autonomic neuropathy and anthropometric and metabolic parameters. Methods: This was a monocentric, cross-sectional, observational study conducted at the Endocrinology and Metabolic Disorders Clinic of Alexandrovska Hospital in Sofia. Main methods included detailed clinical and anthropometric assessments, diagnosis of peripheral neuropathy via the Neuropathy Disability Score (NDS), evaluation of cardiac autonomic neuropathy using heart rate variability analysis and Ewing cardiovascular reflex tests, comprehensive laboratory investigations with fasting blood samples, and measurement of serum DEFA3 and DEFA5 levels by ELISA kits. Results: Serum DEFA3 and DEFA5 levels did not differ significantly between patients with T2DM and controls without carbohydrate disturbances, nor by sex or menopausal status. Patients with diabetic nephropathy showed significantly higher levels of both DEFA3 (345.7 ± 77.9 pg/mL vs. 299.2 ± 100.3 pg/mL; p = 0.042) and DEFA5 (5.3 ± 10.1 pg/mL vs. 2.9 ± 2.9 pg/mL; p = 0.044). DEFA5 levels were also elevated in participants with increased albumin-to-creatinine ratio (4.9 ± 9.9 pg/mL vs. 2.2 ± 1.5 pg/mL; p = 0.043). No significant differences were observed in patients with peripheral neuropathy, cardiac autonomic neuropathy, retinopathy, or macroangiopathy, although a non-significant trend toward higher values was noted. DEFA3 demonstrated moderate discriminatory ability for diabetic nephropathy (AUC = 0.641; p = 0.037), superior to DEFA5 (AUC = 0.570; p = 0.303). DEFA3 showed multiple weak positive correlations with diabetes duration, body weight, BMI, total and LDL-cholesterol, serum creatinine, and uric acid, while DEFA5 correlated only with total cholesterol. Conclusions: Circulating DEFA3 and DEFA5 are associated with diabetic nephropathy and selected metabolic and renal parameters in patients with type 2 diabetes, with DEFA3 showing moderate discriminatory capacity. The associations were largely attenuated after covariate adjustment, suggesting that these alpha-defensins likely reflect downstream innate immune activation and renal stress rather than acting as independent drivers of complications.

Background/Objectives: Diabetic neuropathy (DN) is one of the most common complications of type 2 diabetes mellitus (T2DM), involving complex metabolic, vascular, and epigenetic mechanisms. MicroRNA-210-3p (miR-210-3p), a hypoxia-responsive molecule, has been implicated in various diabetic complications, but its role in DN is not well defined. This study aimed to investigate the relationship between miR-210-3p expression, measured as delta Ct (ΔCt), and the presence and type of diabetic neuropathy, as well as correlations with corneal nerve parameters assessed by corneal confocal microscopy (CCM). Methods: Eighty patients with T2DM were stratified into four groups: no neuropathy, autonomic neuropathy, peripheral neuropathy, and combined neuropathy. Expression of miR-210-3p was quantified using RT-qPCR, and CCM was used to measure corneal nerve fiber density (CNFD), length (CNFL), and branch density (CNBD). Results: ΔCt values were significantly lower in patients with combined neuropathy compared to those without neuropathy, indicating higher miR-210-3p expression. Intermediate values were observed in autonomic and peripheral neuropathy groups. CCM parameters were significantly reduced in patients with DN. ΔCt was inversely correlated with neuropathy severity but positively associated with diabetes duration. Conclusions: These findings suggest that miR-210-3p may serve as a biomarker of nerve damage and cellular stress in diabetes, and that combining gene expression profiling with CCM could improve DN diagnosis and monitoring.